Between stations with a quick discontinuous motion

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between stations with a quick discontinuous motion; and (3) asynchronous transport, in which work units are moved independently rather than synchronously between stations. 15.7 To cope with product variety, three types of assembly line are described in the text. Name the three types and explain the differences between them. Answer : The three types of assembly line are (1) single model line, in which only one product is made and there is no variation in the product; (2) batch model line, in which each type of product is produced in batches and the line setup is changed over between each batch; and (3) mixed model line, in which different models are produced simultaneously on the same line but no changeover is required between models. 15.8 What does the term line efficiency mean in production line terminology? Answer : Line efficiency is the proportion uptime on the production line. It is the ratio of the theoretical cycle time T c to the actual average production time T p when downtime on the line is averaged in. 101
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Assembly Lines-3e-S 07-05/06, 06/04/07 15.9 The theoretical minimum number of workers on an assembly line w * is the minimum integer that is greater than the ratio of the work content time T wc divided by the cycle time T c . Two factors are identified in the text that make it difficult to achieve this minimum value in practice. Name the two factors. Answer : The two factors are (1) repositioning losses, in which either the worker or the work unit must be positioned at the start of each work cycle, and (2) the line balancing problem, which refers to the difficulty encountered in allocating all of the work elements in the work content time equally among workers on the line. 15.10 What is the difference between the cycle time T c and the service time T s ? Answer : The cycle time T c is the time interval between arrivals of work units at a station, while service time T s is the actual amount of time available at the station to perform the assigned task. The difference is the repositioning time T r . That is, T s = T c T r . 15.11 What is a minimum rational work element? Answer : As defined in the text, a minimum rational work element is a small amount of work that has a specific limited objective, such as adding a component to the base part or joining two components. A minimum rational work element cannot be subdivided any further without loss of practicality. 15.12 What is meant by the term precedence constraint ? Answer : Precedence constraints are restrictions on the order in which the work elements can be performed. Some elements must be done before others. For example, to create a threaded hole, the hole must be drilled before it can be tapped. 15.13 What is meant by the term balance efficiency ? Answer : The balance efficiency E b is the work content time divided by the total available service time on the line. It can be computed as E b = T wc / wT s , where T wc = work content time, min; T s = the maximum available service time on the line (Max{ T si }), min/cycle; and w = number of workers.
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